1. Field of the Invention
This invention relates to an elevator control apparatus, and more particularly, to an apparatus for controlling an elevator by using a load weighing device.
2. Description of the Related Art
In a control apparatus for an elevator, improvements in electronic and electric control devices employed as subsystems have recently been made due to the development of microelectronics and power electronics. Furthermore, the performance of mechanical portions of the elevator has been also improved due to the development of mechanical engineering. For example, a high-efficiency worm gear, a helical gear and the like have been used in a hoist of an elevator in order to promote a further saving of electricity and energy. An elevator using such a hoist has a load weighing device to control with high efficiency loads on the side of an elevator car at the time when the elevator is started, operated and stopped, that is, loads ranging from no load to a rated load.
The first function of this load weighing device is to detect a load in an elevator car, add a torque corresponding to the load to a motor torque previous to the operating of the elevator, improve the riding quality at the time when the elevator car is started, operated and stopped, and improve the landing accuracy. The second function thereof is to control the operation of the elevator car in accordance with the load therein. For example, if too many passengers get into the elevator car the load weighing device informs the passengers and makes the elevator car pass a number of floors at which it usually stops. The number of floors that the elevator passes depends on the percentage of the passengers in the elevator car. The load weighing device also assigns a not-full elevator from a plurality of elevator cars. A load weighing device that causes the elevator car to pass floors at which it normally stops is called a control weighing device.
FIG. 7 shows this kind of conventional elevator control apparatus.
Referring to FIG. 7, the control apparatus is provided with a sheave 11, a rope 12 hung on the sheave 11, a counterweight 13, a car frame 14 connected to the rope 12 through a shackle spring (not shown) at the tip of the rope 12, a cage 15 located in the car frame 14, a rubber vibration insulator 16 supporting the cage 15, a load weighing device 17 disposed parallel to the rubber vibration insulator 16 for outputting a predetermined signal 17a, a cable 18, such as a power line or a signal line, for supplying electric power to an elevator car and also transmitting and receiving signals to and from the elevator car, a drive motor 19 for driving the sheave 11, a power converter device 20 for driving the motor 19, a microcomputer 21 at the core of the operation control and administration of the elevator for outputting a torque command 21a to the power converter device 20. Numerals 22, 23 and 24 denote the top floor, the center floor in the center of the whole elevation path, and the bottom floor, respectively.
In the control apparatus, the weight of the cage 15 and passengers and loads in the cage 15 are detected by the load weighing device 17. The load-weighing device 17 generally has a plurality of contacts, and when passengers get into the cage 15 the rubber vibration insulator 16 is bent and some of the contacts are turned in accordance with the amount of bending. These plurality of contacts are set to be gradually actuated at, for example, 25%, 50%, 75%, 110% and so on of a rated load, respectively. The signal 17a is output from each of the contacts to the microcomputer 21.
The microcomputer 21 functions as the core of the operation control and administration of the elevator and gives instructions regarding the registration, illuminating and extinguishing of the lights of floor buttons and cage buttons. The microcomputer 21 also controls the closing of the door, the starting, operating and stopping of the elevator car, and supplies a proper torque command 21a for the operating of the elevator to the power converter device 20 for driving the motor 19.
According to the elevator control apparatus having the above construction, for example, if too many passengers get into the cage 15, the weight Of the cage 15 and the passengers exceeds the rated load, a 110% contact of the load weighing device 17 is turned on, and then a signal 17a is output from the contact to the microcomputer 21. The microcomputer 21 informs the passengers that there are too many passengers by a buzzer or the like, and gives a command to keep the elevator door open.
In the case of a high-efficiency hoist, an unbalanced torque of a sheave shaft causes riding quality to become worse. Although the unbalanced torque of the sheave shaft includes the unbalanced rope weight on the sides of the elevator car and the counterweight and a torque corresponding to the weight of the cable 18 in addition to a torque corresponding to the load in the elevator car, the conventional load weighing device 17 cannot detect the unbalanced rope weight, the weight of the cable 18 and so on. The cable 18 contains power lines and signal lines which are connected to the elevator car and are heavy. Therefore, it is impossible to precisely compensate the unbalanced torque of the sheave shaft based on only the output of the load weighing device 17. As a result, the weight of the rope 12 and the cable 18 is not compensated when the elevator car starts to move, and a sufficient riding quality is not obtained. Furthermore, it is difficult to obtain a sufficient riding quality as regards the landing of the elevator car and the landing accuracy for the same reason as given above.